The 5★ Welcome Idol Chance is added directly into your inventory, so please try to check your Bag.
To access your Bag, open your in-game smartphone, then select [Bag].
Furthermore, the following items will be distributed by logging in after 5:00 JST (20:00 UTC for the English version) the day after the purchase was made.
Logging in for two days: 10x Gold Tickets
Logging in for three days: 1x 4★ Weapon Case